Catalytic bleaching process



Patented Aug. 30, 1949 \UNETED STATES PATENT @FFHQ CATALYTIC BLEACHING PROCESS Robert M. Levy and James E. Brennan, Brevard, N. 0., assignors to Ecusta Paper Corporation, a

corporation of Delaware No Drawing. Application-ctober 14, 1948, Serial No. 54,571

6 Claims.

1 In the production of bleached pulp for high quality cigarette paper, a major problem is to obtain a pulp without deleteriously affecting the important physical properties, particularly the wet-strength, of the final paper produced from.

the bleached pulp. An illustrative exampleris high quality cigarette paper that requires high wet-strength to render it resistant to disintegration in the smokers mouth. Long or drastic bleaching of the pulp normally results in the break down of the physical characteristics in the final paper.

.Anobject of our invention is to bleach'cigarette paper pulp insuch a manner as to produce high wet-strength cigarettepaper and maintain-the other'important physical characteristics.

From the extensive research leading to our invention we have observed that the viscosity of the pulp influences the dry strength and fold characteristics of the finished paper, and that the copper number of the pulp substantially controls the wet-strength of the final-cigarette paper. These characteristics vary generally in proportion to the value of the viscosity and copper numbers, respectively; and the-normal tendency encountered is for the viscosity to decrease-as" the copper number increases. Accordingly, with theusual bleaching processes, it is not'feasible to maintain the viscosity of the pulp at a high value and at .-the same time obtainthe high copper number that is attendant to desired high wet-strength.

In accordance with our invention'we have discovered-acatalyticbleaching process that enables -us to control the viscosity-copper number relationship of the pulp and thereby obtain in the final paper the desired physial characteristics .that result from or accompany this optimum relationship. More specifically, our process makes it-possible. tomaintaina relatively high viscosity inthe pulp and at the same time obtaina relatively. high copper number. A representative but non-limiting exampleiotthe desirable values that are obtained at the same time and in the same pulp, by means of our invention, is:

Viscosity 18 -(Standard TAPPI cuprammonium viscosity T 206 M37) Copper Number '2 (TAPPI II 215-.-M 32) When using arconventional bleaching method it is possible to obtain one nor the other of the above values, but not bothsimultaneously in the same pulp, and therefore the .pulp will .be .de-

ificient in one or more of the desirable physical characteristics. For example, inrtherusual case of apulplhavinga viscosity of .16 orabove, the

:copper .number will be less than 1, and the finished paperwill not have the desirable high wet- .strength.

The catalytic bleaching process that We have discovered and the details of which are described hereafter, comprises the controlled introduction of water soluble salts of cobalt o nickel into a pulp suspension in the-presence of an alkaline bleach solution, such as for example, sodium or calcium hypochlorite. The pulp stock is bleached by the reaction products of the hypochlorite and the metallic salt, under certain important conditionsthatwe have found and are described hereafter.

-We' wish-to protect broadly as our invention,

our discovery of the employment of these metallic "saltsaccording to -a critical procedure for obtaining-simultaneously the desired high viscosity-high copper numbervalues in thebleached cigarette p p pu p- Commercially advantageous examples of these catalytic "salts are the water soluble chloride,

sulfate and nitrate salts of cobalt or nickel.

When an aqueoussolution of a cobaltous salt is treated-with a calcium hypochlorite solution the probable reaction-that takes placeis represented by the following:

C0++Cl2+ alkaline bleach liquor Co+++ (OH) 3+CaClz The reactiontmost probably takes place in two ,steps thus:

"The cobaltic hydroxide, Co(OH)s, which is finally produced in the reaction, has a distinctive black color and we believe that this black cobaltic hydroxide is the effective compound, and that it reacts with the hypochlorite to effect further breakdown thereof with liberation of active oxygen-as follows:

prerequisite to the optimum efficiency of our process and to the desirable bleached cigarette paper pulp product having high viscosity-high wet strength and otherdesirable physical characteristics.

These conditions are:

(a) Combining of 'the catalyst solution with the bleaching solution (hypochlorite) before the catalyst is added to the pulp; or addition of the bleaching solution to the pulp before the catalyst is introduced into the pulp;

(2)) Low concentration :of the catalyst-bleaching solution before incorporation into the pulp suspension;

() Control of the amount of catalyst used.

Considering now more specifically the above important conditions, We have observed that if the catalyst is added to the pulp before it is mixed with the bleaching solution, the black cobaltic hydrate is not formed, and we do not obtain the desired relatively high, copper number-viscosity ratio; This result is persuasive of our above mentioned theory that the black cobaltic hydrate, when formed, reacts further with the bleaching solution with the liberation of active oxygen that facilitates the bleaching operation to give the desired characteristics of the pulp. In this con- 7 nection, we have also observed that the catalyst may be added separately to the pulp suspension provided the bleaching solution has already been introduced into the pulp suspension.

The efiiciency of the catalyst is dependent to a very high degree on the extent of the catalyst surface which is in turn controlled by the particle size of the precipitated cobalt hydrate. In fact,

We find that the surface area or particle size of such'catalyst is almost directly proportional to the dilution of the bleaching solution to which it is added. When a soluble cobalt salt is mixed with a dilute bleach liquor, the cobalt hydrate thus formed does not agglomerate but becomes very finely dispersed in perhaps colloidal sized particles having extremely great surface area,

' which condition renders the catalystextremely active. On the contrary,'if the catalyst is prepared in concentrated solution or mixed with a relatively small amount of bleaching solution before it is added to the pulp suspension, it'will not disperse finelyand upon standing will tend to agglomerate and lose much 01 its activity because of the decrease in surface area From the economic standpoint, scientific control ofthe amount of catalyst used is important. In this respect we have found that the copper number-viscosity relationship, at any given chlorine consumption for the pulp, is directly proportional to the amount of catalyst up to a certain maximum. In the case of cobalt, we find that this maximum amount, from the efficiency standpoint, is about 0.033 cobalt based upon the dry weight of the pulp. Typical illustrative examples of this important feature of our process are illustrated by the following data which are based upon one specific type of pulp although these values may vary appreciably with other pulps:

6 5a? Viscosity Copper N o.

In addition to the above important conditions, a, b and c, we find it advantageous to use a starting pH in the neighborhood of the neutral point. Similarly, high consistency of the stock will assist in obtaining the desired high viscosityhigh copper number effect. At a viscosity of 19 it was found, using 0.03% cobalt, that for the same amount of chlorine the copper number increased about 50% for each 3% rise in consistency in the range of 3% to 9%. It is accordingly advantageous to maintain the consistency of the pulp as high as practically possible and still permit proper handling and uniform bleaching of a the pulp.

example, a flax fiber pulp that requires a bleaching time of about 6 to 12 hours (depending upon a number of variables in the pulp) with the conventional bleaching processes, will require only about 1 to 4 hcurswhen bleached according to the catalytic process of our present invention. While shortening of the time of bleaching may economically be a most desirable factor, we find that it is not the controlling influence in obtaining the high copper number-high viscosity values and other desirable properties of the pulp produced by our process.

The cigarette paper pulp used in the process of our invention is advantageously made from flax fiber, but it may be made from various other fibers, such as for example, hemp, ramie,'mani1la, crotalaria, caroa, Phormium tenor, sisal, jute, or mixtures thereof. In general, the bast fibers from stalks and stems of dicotyledonous plants,

and the vascular bundles from leaf fibers of monocotyledonous plants, may be used.

For guidance in carrying out the process of our invention we give the following illustrative example of a satisfactory commercialoperation,

-' for treatment of flax fiber pulp that has been digested, chlorinated and Washed and is ready for bleaching with hypochlorite. Such pulp may be used in the manufacture of high quality cigarette paper. The materials and conditions used in this example may vary substantially and the benefits of our discovery still obtained. We, therefore, do not intend to be limited to this specific embodiment.

For treatment of about 1300 to 1400 kilograms of the above mentioned pulp in a Bellmer or other suitable bleaching equipment, we first prepare the cobalt catalyst by dissolving 2.15 kilograms of CoClafiHzO in about 4 liters of water The resulting solution is filtered to remove any foreign matter. This amount of cobaltous chloride corresponds to approximately 0.03% cobalt of the dry weight of the pulp to be bleached.

This freshly prepared cobaltous chloride solution is poured into a mixing tank or tanks containing about 2100 liters of diluted calcium hypochlorite solution which contains about 10 grams of available chlorine per liter of solution. These two solutions are then mixed thoroughly and the resulting mixture promptly run into the pulp stock suspension in the Bellmer. The catalyst becomes finely dispersed in the diluted bleaching solution. Nevertheless, it is advisable to use'the hypochlorite-catalyst solution within a relatively short time, such as about 10 to 15 minutes after 5 ing solution and to introduce the resulting mixture into the pulp suspension. Y

When the bleaching solution-cobalt catalyst mixture is run into the pulp suspension, which is preferably circulated'in the Bellmer or otherwise agitated during the bleaching process, the added solution promptly discolors'the pulp stock and turns it a brownish-gray color. The consistency of the stock in this specific case is about 5% and the amount of bleaching solution added corresponds to about 1.6% available chlorine, based upon the dry weight of the pulp.

After this addition of the catalyzedbleaching solution, the stock suspension is allowed to remain in contact with it until substantially all of the available chlorine has been exhausted. As above indicated, this exact time will vary with the amount of catalyst, condition of the stock, pH, etc. When the residual chlorine reaches a value of about 0.1 gram'per liter of available chlorine the chlorine supply is substantially exhausted and therefore the bleaching operation is substantially complete.

When this bleaching operation has been completed, the resulting bleached stock suspension is treated with sulfuric acid or other suitable sulfite to convert the cobaltic hydrate into a water soluble cobalt salt. This conversion is evidenced, upon addition of the acid, by the fact that the discolored stock quickly turns white. The stock is mixed or agitated for about 20 minutes for the purpose of completely dissolving the hydrated cobalt oxide.

At the completion of this last step, the pulp is greatly diluted with water to a dilution of about 300 parts of water to one part of pulp, and this diluted suspension is run onto a Vacuum washer where the solubilized cobalt salt is washed out and removed from the stock. The resulting bleached stock is then ready for the conventional refining operations and the making of high quality cigarette paper on a paper-making machine.

Various modifications and changes may be made in the foregoing process, materials and conditions without departing from the scope of our invention, some of the novel features of which are defined in the appended claims.

This application is a continuation-in-part and takes the place of our application Serial No. 527,141, filed March 18, 1944, and allowed on April 15, 1948 but now forfeited.

We claim:

1. In a method of producing cigarette paper which comprises the steps of digesting, chlorinating, bleaching fiax pulp, sheeting the pulp on a paper machine and drying the sheet, the improvement of modifying the bleaching treatment so as to produce a flax pulp having a relatively high copper number for any given viscosity whereby the cigarette paper produced from such pulp will have a wet strength which is relatively high for any given dry strength of the paper, said improved bleaching treatment comprising introducing into an aqueous suspension of the pulp for the bleaching thereof the reaction product of an hypochlorite with a water soluble salt of a metal selected from the group consisting of cobalt and nickel. said hypochlorite being selected from the group consisting of alkali and alkaline earth hypochlorites, and the said reaction product being water insoluble, maintaining the pulp and reaction product in intimate active contact until the desired degree of bleaching is obtained and the pulp has relatively high copper number for any given viscosity, converting said water insoluble reaction product into a water soluble compound, and washing out the water soluble compound.

2. In a method of producing cigarette paper which comprises the steps of digesting, chlorinating, bleaching flax pulp, sheeting the pulp on a paper machine and drying the sheet, the improvement of modifying the bleaching treatment so as to produce a flax pulp having a relatively high copper number for any given viscosity whereby the cigarette paper produced from such pulp will have a relatively high wet strength for any given dry strength of the paper, said improved bleaching treatment comprising reacting dilute aqueous solutions of an hypochlorite selected from the group consisting of alkali and alkaline earth hypochlorites and a water soluble salt of a metal selected from the group consisting of cobalt and nickel, introducing the resulting reaction solution into an aqueous suspension of the pulp for bleaching thereof, maintaining this mixture until the desired degree of bleaching is obtained and finally removing the reaction products.

3. In a method of producing cigarette paper which comprises the steps of digesting, chlorinating, bleaching cigarette paper pulp, sheeting the pulp on a paper machine and drying the sheet, the improvement of modifying the bleaching treatment so as to produce a cigarette paper pulp having a relatively high copper number for any given viscosit whereby the cigarette paper produced from such pulp will have a relatively high wet strength for any given dry strength of the paper, said improved bleaching treatment comprising reacting dilute aqueous solutions of an hypochlorite selected from the group consisting of alkali and alkaline earth hypochlorites and a water soluble salt of a metal selected from the group consisting of cobalt and nickel, introducing the resulting reaction solution into an aqueous suspension of the pulp for bleaching thereof, maintaining this mixture until the desired degree of bleaching is obtained and finally removing the reaction products.

4. In a method of producing cigarette paper which comprises the steps of digesting, chlorinating, bleaching cigarette paper pulp, sheeting the pulp on a paper machine and drying the sheet, the improvement of modifying the bleaching treatment so as to produce a cigarette paper pulp having a relatively high copper number for any given viscosity whereby the cigarette paper produced from such pulp will have a wet strength which is relatively high for any given dry strength of the paper, said improved bleaching treatment comprising introducing into an aqueous suspension of the pulp for the bleaching thereof the reaction product of an hypochlorite with a water soluble salt of a metal selected from the group consisting of cobalt and nickel, said hypochlorite being selected from the group consisting of alkali and alkaline earth hypochlorites, and the said reaction product being water insoluble, maintaining the pulp and reaction product in intimate active contact until the desired degree of bleaching is obtained and the pulp has relatively high copper number for any given viscosity, converting said water insoluble reaction product into a water soluble compound, and washing out the water soluble compound.

5. A catalytic process of bleaching cigarette paper pulp to give the pulp a relatively high copper number for any given viscosity so that the cigarette paper produced from such pulp will have a relatively high Wet strength for any given dry strength of the paper, comprising introducing into an aqueous suspension of said cigarette paper pulp an hypyochlorite selected from the group consisting of alkali and alkaline earth hypochlorites, and then introducing into said pulp and hypochlorite mixture, a dilute aqueous solution of a water soluble salt of a metal selected from the group consisting of cohalt and nickel, and maintaining the reaction products between said hypochlorite and said water soluble salt in intimate active contact with the pulp until the desired degree of bleaching is obtained, and finally removingthe reaction products.

6. A catalytic process of bleaching cigarette paper pulp to give the plup a relatively high copper number for any given viscosity so that the cigarette paper produced from such pulp will have a relatively high Wet strength for any given dry strength of the paper, comprising mixing dilute aqueous solutions of an hypochlorite selected from the group consisting of alkali and alkaline earth hypochlorites and a water soluble salt of a metal selected from the group consisting of cobalt and nickel, then introducing this mixture into an aqueous suspension of the cigarette paper pulp for bleaching thereof, maintaining 8 this mixture until the desired degree of bleaching is obtained and finally removing the reaction products.

ROBERT .M. LEVY.

OTHER. 7 REFERENCES 7 Hall, Monthly Review, Textile Colorist, Jan. 1938, page 39.

Sutermeister, Chemistry of Pulp and Paper Making, third ed, 1941, John Wiley 8: Sons, New York, page 274a 

